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How to Charge Millions of Electric Cars? Not All at Once

¶ PROPONENTS of electric vehicles like to talk about a not-too-distant future when plug-in cars become ubiquitous, with millions being driven by their owners on the daily commute.

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¶ Now imagine the end of a workday in that not-too-distant future, when many of those millions of cars are back in their owners’ driveways or garages, plugged in for battery recharging, all at roughly the same time.

¶ The effect of such a power drain on the electrical grid could be enormous; the overloading of transformers and other infrastructure could lead to local brownouts or worse. So researchers at utility companies and other electrical engineers are looking for ways to soften the blow, designing charging systems that can adapt quickly to changing grid conditions.

¶ These programmable systems could help save customers money by allowing them to charge their cars at lower electricity rates, but experts say they can also improve the stability of the grid and help it better adapt in the event sources of power with great variability, like wind and solar energy, become a larger part of the supply.

¶ “It’s good for the industry and it’s good for your pocketbook,” said Michael Kintner-Meyer, an engineer at Pacific Northwest National Laboratory in Richland, Wash.

¶ The efforts are related to work on the so-called smart grid. Its goal is to more efficiently manage power supply and demand through instantaneous data collection on electricity generation and usage, incentive pricing and other methods.

¶ Although there are fewer than 100,000 plug-in cars in the United States, they eventually could play an important role in the smart grid because they are flexible when it comes to charging, said Mr. Kintner-Meyer, who with colleagues at the laboratory has worked on “grid friendly” systems.

¶ Depending on battery size and how much the car is driven, a plug-in electric can increase a house’s power consumption by 50 percent or more. But unlike other power-hungry equipment — notably air-conditioners and refrigerators — cars usually sit idle 12 or more hours at night and, especially with higher-voltage charging systems, need only some of that time to fully recharge.

¶ “There’s enough flexibility in the charging duration so you can move the load around,” Mr. Kintner-Meyer said.

¶ With the right incentives — lower electricity rates for off-peak periods, which some utilities already offer — customers can be induced to program their chargers to operate later in the night, relieving some of the load on the grid. But off-peak savings are really just a beginning. At San Diego Gas and Electric, which has one of the highest concentrations of plug-in electric cars of any utility in the United States (4,000 owned by its customers), researchers are working on a system that will take advantage of rapid changes in the price of electricity throughout the day as supply and demand fluctuate.

¶ “You could tell your car to charge when the price gets to a certain level,” said James P. Avery, the utility’s senior vice president for power supply. Power could be cheaper “when the sun comes out or the wind blows,” he said, increasing the supply from wind turbines or solar arrays.

¶ At Pacific Northwest National Laboratory, Mr. Kintner-Meyer and his colleagues designed a plug-in charger that monitors the condition of the electric grid and can alter its charging pattern in response


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